Sift together dry ingredients. Set aside. Cream together remaining ingredients until lighter in color. Slowly add flour mixture; mix until well incorporated. For each cookie, roll a level tablespoon of dough into a smooth ball. Place cookies on greased baking sheet, placing them 2 inches apart. Use a fork to gently flatten the cookies into 1-1/4 inch disks; make an impression with the fork tines in the top of each. Bake about 30 minutes. The cookie bottoms will be lightly browned. Cool on the baking sheets for 10 minutes. Transfer cookies to rack and let cool completely.

Buttercream filling:

1/4 cup (2 ounces) butter

3/4 cup powdered sugar

1 teaspoon vanilla extract

1/2 ounce dark chocolate, melted (optional)

In a medium bowl, use a large spoon to stir the butter, powdered sugar, and vanilla until smooth. Stir in melted chocolate, if desired.

Turn half of the cookies bottom side up. Use a thin metal spatula to spread a rounded teaspoon of filling evenly over the flat bottom of each. Gently press the flat bottom of the remaining cookies on the filling.

Serve at room temperature. Makes about 12 sandwiches (24 cookies). Cookies can be stored in an air tight container at room temperature for up to 5 days.